A method for writing information on a highly coercive recording medium stably with an electric field applied through a metal probe and with a magnetic field applied from external and an information recording system that employs the method. The recording medium includes a substrate, a first ferromagnetic layer formed on the substrate, a nonmagnetic layer formed on the first ferromagnetic layer, and a second ferromagnetic layer formed on the nonmagnetic layer. The coercivity Hc2 of the second ferromagnetic layer is larger than that Hc1 of the first ferromagnetic layer. A magnetic field H is applied to the magnetic recording medium from a magnetic pole to change the magnetizing direction of the first ferromagnetic layer to a direction of the applied magnetic field, then a positive or negative voltage V is applied between the metal probe and the magnetic recording medium to change the quantum well level energy between the first and second ferromagnetic layers, thereby inducing an exchange magnetic field HE. As a result, the magnetizing direction of the second ferromagnetic layer is changed with both the exchange magnetic field HE and the magnetic field H.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A magnetic recording system comprising: a magnetic recording medium including a substrate, a first ferromagnetic layer formed on said substrate, a nonmagnetic layer formed on said first ferromagnetic layer, and a second ferromagnetic layer formed on said nonmagnetic layer; a magnetic pole for applying a magnetic field H to invert a magnetizing direction of said first ferromagnetic layer; and means for applying a positive or a negative voltage V between a metallic probe and said magnetic recording medium, wherein a coercivity Hc 2 of said second ferromagnetic layer is larger than that Hc 1 of said first ferromagnetic layer; wherein a quantum well level is formed in said nonmagnetic layer formed between said first and second ferromagnetic layers; wherein said magnetic field H changes said magnetizing direction of said first ferromagnetic layer to a direction of an applied magnetic field; wherein applying said positive or negative voltage V changes an energy of said quantum well level between said first and second ferromagnetic layers, thereby inducing an exchange magnetic field H E ; and wherein said magnetic field H and said exchange magnetic field H E work together to invert said magnetizing direction of said second ferromagnetic layer.
2. The magnetic recording system according to claim 1 , wherein said coercivity Hc 1 of said first ferromagnetic layer, said coercivity Hc 2 of said second ferromagnetic layer, and said magnetic field H are in a relationship of Hc 1 <H<Hc 2 ; and wherein said exchange magnetic field H E has a relationship of Hc 2 <H+H E with said coercivity Hc 2 of said second ferromagnetic layer and said magnetic field H.
3. The magnetic recording system according to claim 2 , wherein said exchange magnetic field H E has a relationship of H-H E <Hc 1 with said coercivity Hc 1 of said first ferromagnetic layer and said magnetic field H.
4. The magnetic recording system according to claim 1 , wherein said first ferromagnetic layer is formed on an antiferromagnetic layer and magnetization of said first ferromagnetic layer is fixed.
5. The magnetic recording system according to claim 1 , wherein said first and second ferromagnetic layers are magnetized in a longitudinal direction respectively.
6. The magnetic recording system according to claim 1 , wherein said first and second ferromagnetic layers are magnetized in a direction perpendicular to their film surfaces respectively.
7. The magnetic recording system according to claim 1 , wherein said magnetic recording medium further includes: a third ferromagnetic layer formed between said first ferromagnetic layer and said substrate through a nonmagnetic layer; and an antiferromagnetic layer formed between said substrate and said third ferromagnetic layer.
8. The magnetic recording system according to claim 1 , wherein a magnetic exchange interaction that works between said first and second ferromagnetic layers is almost zero while said positive or negative voltage V is not applied.
9. The magnetic recording system according to claim 1 , wherein said positive or negative voltage is applied between the metallic probe and a surface of a magnetized region and said magnetizing direction of each of said ferromagnetic layers is read according to a change of a tunnel current value.
10. A magnetic recording system, comprising: a magnetic recording medium including a substrate, a first ferromagnetic layer formed on said substrate, a nonmagnetic layer formed on said first ferromagnetic layer, and a second ferromagnetic layer formed on said nonmagnetic layer; a magnetic pole for applying a magnetic field H to invert a magnetizing direction of said first ferromagnetic layer; and an electrode for applying a positive or negative voltage V between a metallic probe and said magnetic recording medium, wherein a coercivity Hc 2 of said second ferromagnetic layer is larger than that Hc 1 of said first ferromagnetic layer; wherein said magnetic field H changes said magnetizing direction of said first ferromagnetic layer to a direction of an applied magnetic field; and wherein applying said positive or negative voltage V inverts said magnetizing direction of said second ferromagnetic layer, thereby recording magnetization information in said second ferromagnetic layer.
11. The system according to claim 10 , wherein application of said positive or negative voltage V induces an exchange magnetic field H E ; and wherein said exchange magnetic field H E and said magnetic field H work together to invert said magnetizing direction of said second ferromagnetic layer.
12. The magnetic recording system according to claim 10 , wherein said coercivity Hc 1 of said first ferromagnetic layer, said coercivity Hc 2 of said second ferromagnetic layer, and said magnetic field H are in a relationship of Hc 1 <H<Hc 2 ; and wherein said exchange magnetic field H E has a relationship of Hc 2 <H+H E with said coercivity Hc 2 of said second ferromagnetic layer and said magnetic field H.
13. The magnetic recording system according to claim 12 , wherein said exchange magnetic field H E has a relationship of H-H E <Hc 1 with said coercivity Hc 1 of said first ferromagnetic layer and said magnetic field H.
14. An electric field applying magnetic recording method comprising the steps of: applying a magnetic field H from a magnetic pole to a magnetic recording medium composed of a substrate, a first ferromagnetic layer formed on said substrate, a nonmagnetic layer formed on said first ferromagnetic layer, and a second ferromagnetic layer of which coercivity Hc 2 is larger than that Hc 1 of said first ferromagnetic layer, formed on said nonmagnetic layer, thereby changing a magnetizing direction of said first ferromagnetic layer to a direction of said applied magnetic field; applying a positive or negative voltage V between a metallic probe and said magnetic recording medium to change an energy of a quantum well level between said first and second ferromagnetic layers, thereby inducing an exchange magnetic field H E ; and changing a magnetizing direction of said second ferromagnetic layer to a direction of said applied magnetic field with both said exchange magnetic field H E and said magnetic field H.
15. The method according to claim 14 , wherein said coercivity Hc 1 of said first ferromagnetic layer, said coercivity Hc 2 of said second ferromagnetic layer, and said magnetic field H are in a relationship of Hc 1 <H<Hc 2 ; and wherein said exchange magnetic field H E has a relationship of Hc 2 <H+H E with said coercivity Hc 2 of said second ferromagnetic layer and said magnetic field H.
16. The method according to claim 14 , wherein said exchange magnetic field H E has a relationship of H-H E <Hc 1 with said coercivity Hc 1 of said first ferromagnetic layer and said magnetic field H.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
July 27, 2007
January 4, 2011
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